During a double Fortuna substitution, Jasper Dahlhaus only temporarily left the pitch before re-entering in front of the fourth official. With no intervention from the officiating crew, Fortuna were allowed to play on with twelve players on the pitch for 25 seconds.
After the ball went out of play for a throw-in, the referee stopped the game and let Alen Halilovic - who was actually meant to get taken off - leave the pitch on the opposite side. The throw-in got followed up by a corner for Fortuna Sittard, which the visitors would convert and turn into an 89th-minute equaliser.
This much to the dismay of Heerenveen manager Robin van Persie, who called the officials "amateurs" as it happened. "Twelve against eleven. I didn't know that was allowed, but apparently you can just do it," Van Persie stated after the game.
A day after the incident, the Dutch football association KNVB announced it would seek advice from the IFAB to see what retrospectively would be possible to do. The KNVB spoke of a "very annoying and exceptionally sloppy situation."
'We have requested the statements on the exact events from the referees and the clubs," the KNVB said on their website.
"Based on those statements, we will seek advice from the IFAB. After we receive that advice, the professional football league board will make a decision."